This research proposal has been designed mainly to study the role of lipid in the function of two proteins of the intestinal brush border membrane, namely rat alkaline phosphatase and the receptor for intrinsic factor-vitamin B12 in dog. Using purified phosphatases from the proximal (membrane bound) and distal (soluble) intestines of suckling rats, we will study the (a) binding of detergents like H3 triton X-100, (b) lipid analysis of the two forms of the enzyme. The membranes from rat and dog will be treated with phospholipases and the digested membranes will be used for kinetic measurement with substrates like phenylphosphate, ATP, and beta-glycerophosphate for alkaline phosphatase and with human and hog IF for the receptor. The effect of addition of specific lipids to the purified proteins will be studied. Purified intestinal alkaline phosphatase and partially purified receptor will be used to reconstitute transport systems for PO4---ions and vitamin B12. Brush border lipids or synthetic lipids will be used to make liposomes. The uptake studies will be done by millipore filtration method. Uptake of PO4 from organic and inorganic sources will be examined in the presence and absence of alkaline phosphatase. The role of different lipids will be studied in the transfer of PO4 (if this is related to phosphatase) and vitamin B12. The effect of both intestinal luminal protease (trypsin, chymotrypsin) and lysosomal cathepsins C and D on the uptake I125 IF- 57 CoB12 by the liposomes will be studied to ascertain the fate of IF after it binds to the receptor. These uptake studies will also be extended to membrane vesicles.